Hard to escape, bad luck is unchanged (4)
I believe the answer is:
same
'unchanged' is the definition.
(similar in meaning)
'hard to escape bad luck' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'to escape' is a deletion indicator.
'bad luck' becomes 'shame' (shame is a kind of bad luck).
'shame' with 'h' removed is 'SAME'.
'is' is the link.
(Other definitions for same that I've seen before include "uniform" , "Ditto" , "Equal in amount or value" , "Aforesaid" , "Identical or similar" .)